This invention relates to camshaft arrangements having cams supported for limited angular motion. German Offenlegungsschrift No. 41 22 251 discloses a camshaft arrangement in which cams supported for limited angular motion are provided with stops formed as claws projecting from a tube extending parallel to the camshaft and held stationary with respect to the cam. Another configuration of cam stops, in which they are beneath the cam rather than extending laterally with respect to the cam, is disclosed in German Patent No. 32 34 640. In that arrangement, the stop is a strip mounted in the camshaft and projecting into an angular recess extending over a selected angle in an inner surface of the cam adjacent to the camshaft so as to define the limits of angular motion of the cam with respect to the camshaft. In one form, the recess is a closed hydraulic system, while in another form a passage having a check valve connects the recess with a passage in the camshaft to provide hydraulic damping fluid to the recess.
The above-mentioned prior art movable cam arrangements provide the advantageous possibility of optimizing an engine valve stroke curve as a function of the rotational speed of the engine during operation. In principle, this is accomplished because the cam is held in fixed position with respect to the camshaft only during certain angular intervals of each camshaft revolution when it rotates at the same speed as the camshaft while, in the other angular intervals, the angular velocity of the cam is greater or less than the rotational speed of the camshaft. Assuming a constant camshaft speed during a revolution, therefore, these arrangements provide angular intervals of uniform and nonuniform rotational motion of the cam.
To the extent that the prior art discloses the use of damping fluid, a longitudinal passage in the camshaft is provided for this purpose, which must, accordingly, be connected to a source of damping fluid. Generally, the lubricating oil supply for the engine is used as the damping fluid and is supplied to the longitudinal passage in the camshaft at a central location in the engine. When the camshaft is comparatively long, however, the flow resistance of the passage may cause pressure losses which adversely affect the damping action in the cam recess. The adverse effect of this pressure loss is especially noticeable when the engine generates a comparatively low oil pressure in its lubricating system as, for example, when it is idling.